Within the field of neurotechnology, deep brain stimulation (DBS) is a surgical treatment involving the implantation of a medical device called a deep-brain stimulator, which sends electrical impulses to specific parts of the brain. DBS in certain brain regions has provided remarkable therapeutic benefits for otherwise treatment-resistant disorders such as chronic pain, Parkinson's disease, tremor and dystonia. Despite the long history of DBS, its underlying principles and mechanisms are still not clear. DBS directly changes brain activity in a controlled manner. Unlike lesioning techniques, its effects are reversible. Furthermore, DBS is one of only a few neurosurgical methods that allow blinded studies.
In principle, the deep brain stimulation system comprises two components: the implanted pulse generator (IPG), and the probe. The IPG is a battery-powered neurostimulator that sends electrical pulses to the brain to interfere with neural activity at the target site. The IPG is typically encased in e.g. a titanium housing. The probe consists of about 10-40 cm long wires and a plurality of electrodes. The wires connect the IPG to the electrodes, which are located at the distal end of the probe. The IPG may be calibrated by a neurologist, nurse or trained technician to optimize symptom suppression and control side effects.
DBS probes are placed in the brain according to the type of symptoms to be addressed. All components are surgically implanted inside the body. The typical procedure is performed under local anaesthesia, where a hole is drilled in the skull and the electrode is inserted with feedback from the patient for optimal placement. The right side of the brain is stimulated to address symptoms on the left side of the body and vice versa.
In stereotactic neurosurgical procedures one often needs to target a small structure in the delicate brain tissue. Frequently, the precise location is not known during the surgical planning stage, either because it is poorly visible on anatomic patient images, such as MRI, or because specific features of interest, such as functionality, cannot be visualized directly by existing medical imaging techniques.
To cope with this uncertainty, a number of parallel trajectories towards the presumed target brain area are often sampled. This is especially important during deep brain stimulator implantation. In this case a tool called Ben's gun, well known to a person skilled in the art, is used to guide five probes through holes along parallel paths to the presumed target area. FIG. 1 is showing top view of a guiding tool 10, currently used in Ben's gun, with five holes 13, shaped as a cross formed by two rows of three holes, with one hole in the centre. The centre hole represents the position, from which the probe has to enter the tissue in a z-direction in order to end up in the target area. The location of the target area, and thus the positioning of the centre hole, is based on MRI scans, and calculated by software when planning the insertion of a probe. However, in order to allow for slight miscalculations, the other four holes, placed around the centre hole at a distance of about 2 mm, allow adjustment of the positioning of the probe in a x- or y-direction at the time when the application is performed. Thus, a correction of 1-2 mm in lateral-medial and posterior-anterior directions can be made with respect to the central path. In DBS procedures Ben's gun is positioned in a so-called micro-drive system, well known to a person skilled in the art, which is used to accurately guide the probes into the brain tissue.
FIG. 2 is showing application of a probe 11 through a cross section of a guiding tool 10 according to prior art, such as Ben's gun. This is applicable when the probe is used temporarily, i.e. not when the probe is to be left inside the tissue, such as in deep brain stimulation (DBS). FIG. 2 A is showing the probe position before entering the tissue. The arrow marks the downward movement of the probe. FIG. 2 B is showing how to extract the probe from the tissue after use. The arrow marks the upward movement of the probe.
FIG. 3 is showing another way of applying a probe 11 through a guiding tool 10 according to prior art, such as Ben's gun. This is applicable when the probe is to be applied and left in the tissue. FIG. 3 A is showing the probe position before entering the tissue. The arrow marks the downward movement of the probe. FIG. 3 B is showing the probe in position inside tissue. FIG. 3 C is showing how to extract the probe from the tissue after use. The arrow marks the sideway motion with which the probe is pulled through the hole, where after the guiding tool 10 may be removed.
The layout of Ben's gun is such that probes guided into the tissue can only be removed from Ben's gun by pulling them back out the way they were inserted. The probe may also be pulled all the way through Ben's Gun. When inserting chronic probes, which is the case in DBS, the only option is to pull probe all the way through Ben's gun which may induce mechanical forces on the probe, with the risk of displacement of the probe in the (deep) brain tissues. Also, the pulling through requires the probe's diameter along its full length to be smaller than the diameter of the holes of Ben's gun. This limits the functionality of the probe at its proximal size since the size of any connector, electronics, or other component that is attached to the proximal end of the probe is constrained by the diameter of the guide.
Hence, an improved tool for guiding neurosurgical probes, allowing for increased flexibility, cost-effectiveness, safety and user friendliness would be advantageous.